Concussion protection for loudspeakers



March 11 1958 A. w. PAGE CONCUSSION PROTECTION FOR LOUDSPEAKERS FiledAug. 4, 1952 J N V ENTOR.

ARTHUR W. PAGE BY 8 g 2 E V fi/zar'kzey United States Patent CONCUSSIONPROTECTION FOR LOUDSPEAKERS Arthur W. Page, Red Bank, N. J., assignor tothe United States of America as represented by the Secretary of the ArmyApplication August 4, 1952, Serial'No. 302,634

2 Claims. Cl. 181-31) (Granted under Title 35, U. S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government for governmental pur-- poses, without the payment ofany royalty thereon.

This invention relates to loudspeakers and particularly to loudspeakershaving a movable diaphragm provided with an external driving means. Moreparticularly, this invention relates to a mechanical means forblastproofing the diaphragm of a loudspeaker.

Loudspeakers are well known in the art and usually comprise a diaphragmin the form of a cone, tapered or corrugated to provide certainacoustical effects and including a driving means, usuallyelectromagnetic and commonly in the form of a thin cylindrical coil,rigidly attached near the apex of the cone and coaxial to the cone. Thisvoice coil is free to move in a strong magnetic field supplied by anelectrodynamic or permanent magnet. The cone is resiliently mounted,near the apex and around its base, to a fixed support coupled to themagnet.

The cone is made of light, relatively thin materialusually some form ofpaperand is only strong enough to be driven by the light force of thevoice coil. The cone has a relatively large area exposed to the air andis inevitably exposed to blast or pressure waves wherever such mayexist. Therefore, a pressure wave of any intensity may tear the fragilecone out of its mountings.

It is an object of this invention to provide a blastproof, cone-typeloudspeaker.

It is a further object of this invention to provide a means forprotecting the diaphragm section of a loudspeaker against shock.

It is a further object of this invention to provide perforated plates oneither side of a loudspeaker diaphragm for protection against excessiveexcursion of the diaphragm. Other objects of the invention will becomeapparent from the specification and claims.

Certain obscure types of loudspeakers have been suggested, as in thepatents to Rice 1,631,646 and Gueritot 1,523,262, where the diaphragmand voice coil have been combined in a unitary cone structure. These areimpractical by modern standards due to the limited size of diaphragm,the cumbersome and ineffective magnetic structure and the uncertainacoustical quality. These types of speakers are almost unknown today andsince they do not teach or refer to blastproofiug in any way, they donot, even broadly construed, provide a practical solution to the problemsolved by applicants device. These speakers will fall in the generalclass of driver units for horns that have such small diaphragms thatblastproofing is not generally requisite.

In the drawings Fig. 1 shows a cross sectional view through the conicalaxis of a typical loudspeaker blastproofed according to the invention.The mounting of the cone, voice coil and protective plates is shown butthe magnetic structure, since it is well known in the art, has beenomitted to simplify the drawing.

Fig. 2 is a view of a standard loudspeaker, such as Fig. 1 would appearas a complete unit.

Referring now to Fig. 1 the cone shaped diaphragm 10 is seen mounted atits base in the ring structure 12 and near its apex by another ringstructure 14 through a supporting spider 16. The spider is a highlycompliant structure allowing a considerable freedom of movement in thedirection of the axis of the cone while holding the cone rigid inlateral directions.

The voice coil 18 is in the form of a thin cylinder and I is rigidlyattached near the apex of the cone. Magnetic: structures such as arewell known in the art would sun round this voice coil and be a part ofthe rigid structure of the loudspeaker, including the rings 14 and 12,seen to better advantage in Fig. 2. The base of the cone includes acorrugated ring 20 or other means, relatively more compliant than therest of the cone, to allow the main portion of the cone 10 to move, inresponse to the voice coil, in an. axial direction.

The excursion of the cone to the rear is limited by mem-- ber 22 and theexcursion of the cone to the front is limited by member 24. Thesemembers are thin plates which: need be of only sufiicient thickness andstrength to withstand the pressure of the diaphragm and the shock wave..The plates would be of any rigid material such as metal: or fiberboardand should be as light as practical to avoid adding unnecessary weightto the speaker and should be non-magnetic to avoid interference with thevoice coil field. Both of these plates are formed to follow theconfigurations of the diaphragm as closely as possible so that thediaphragm in its extreme excursion will seat itself evenly against theseretaining structures.

The outer structure 24 has perforations 26 to allow thepassage of normalsound waves generated by the voice coil. and the element 22 has theperforations 28 to relieve the; back pressure of the diaphragm. Thesound pressure is. also to some extent relieved by the openings 27 and29 near the apex of the cone. These perforations should be of a largeenough size and of sufficient number to pass sub stantially all of thenormal sound pressure of the diaphragm. At the same time, theirdiameter, spacing and number can be chosen to produce certain desirableeffects by their inherent filter action. These retaining plates 22 and24 can be supported by ring 12 along with the rigid structure of theloudspeaker and separated and uniformly spaced from the diaphragm 10 bygaskets 30 and 32.

The two conductors to the voice coil may be brought out in aconventional way across the spider 16 or they may be brought out alongthe surface of the cone 10 to terminals 34 and 36 at any convenientpoints along the outer rim of the loudspeaker.

Fig. 2 shows a rear view of the loudspeaker with outer rim 112corresponding to ring 12 of Fig. 1, and the inner rim 114 rigidlysupported by braces 116 and attached to the magnetic structure 115. Theretaining plate 122 with its perforations 128 can be seen from thisview.

The foregoing describes a preferred embodiment of this invention. Anynumber of mechanical variations of loudspeaker structure, shape of cone,driving elements, etc, will be obvious to those skilled in the art.

What is claimed is:

l. A loudspeaker comprising a diaphragm mounted to permit a normalexcursion thereof between a first and second position, and means forlimiting abnormal excursions of said diaphragm comprising a first,perforated, nonmagnetic retaining wall having a shape which is congruentwith one surface of said diaphragm situated in the vicinity of saidfirst position, and a second perforated, non-magnetic retaining wallhaving a shape which is congruent with the other surface of saiddiaphragm situated in the vicinity of said second position.

2. A loudspeaker having a resiliently mounted diaphragm of substantiallyuniform thickness, said resilient;

Patented Mar. 11, 1958 mounting: permitting va;normal"excursion of saiddiaphragm between a firstand.secondeposition, .and-meansfor preventingabnormal excursions of said diaphragm comprising a first, perforated,non-magnetic retaining structure having; onev-surface. shapedsubstantially like said diaphragm- .and closely spaced: from. one.surface of said" diaphragmin said:fi1'St.positiOI1',.and;a;se'eonct-perforat'ed, nonmagnetic. retaining structure having onesurface sha'ped substantially like sa'id diaphragm and closely spacedfrom the otherr.surface='of'said diaphragm in said-second-posi-References Cited in the file of this patent tion, whereby saiddiaphragmis 'prevented' from moving beyonditsnormal excursion;

UNITED' -STATES PATENTS Stewart Apr. 1, Burch Aug. 26, Wegel Sept. 12,Evans Mar. 20, Marlow -Apr.-. 1 1, Gersch June 20, Olsen-er a1; Oct..23;

FOREIGN PATENTS GreaLBritain Dec. 27,

